Potential of all‐cellulose composites in corrugated board applications: Comparison of chemical pulp raw materials

All‐cellulose composites (ACCs) were produced using various commercially available chemical pulps by partial dissolution method using an aqueous zinc chloride (ZnCl₂) solvent. Characterization methods used for defining material performance, keeping especially corrugated board products in mind, were as follows: scanning electron microscopy, tensile strength, 2‐point bending stiffness, concora medium test, and short‐span crush test. Hardwood (bleached eucalyptus), softwood (bleached spruce, bleached and unbleached pine), speciality softwood pulps (sulphite dissolving with 530 and 398 mL/g intrinsic viscosities), and annual plant pulp (bleached abaca) were investigated to give a broad overview of the potential for making ACCs. Softwood pulps, especially bleached, showed highest increase in mechanical properties across the board. Hardwood pulp showed relatively good results, and the selected annual plant pulp (abaca) responded partially negatively to treatment. Comparing unbleached and bleached softwood ACCs, it seems that bleaching is beneficial for tensile properties. However, when material comes under compressive or bending loads, unbleached pulp performs very well. Comparing sulphite dissolved pulps, it could be proven that pulps with higher intrinsic viscosities, thus higher polymerization grade, respond better to partial dissolution. It was proven that a wide set of pulps, also of lesser cellulose purity, used in the paper industry are viable for ACC production. Furthermore, results from short‐span crush test and concora medium tests show high potential of ACCs for corrugated board applications.     

Preparation of SiC nanopowder using low-temperature combustion synthesized precursor

SiC nanopowder was synthesized by carbothermal reduction of a low-temperature combustion synthesized (LCS) precursor derived from silicic acid, polyacrylamide (PAM), nitric acid, urea, and glucose mixed solution. The results showed that the LCS precursor is a kind of porous blocky particles. The precursors were subsequently calcined under argon at 1100–1500 °C for 2 h. The transformation of SiO₂ to SiC occurred at 1200 °C, and complete transformation of SiO₂ to SiC was achieved at 1500 °C. The SiC powder synthesized at 1500 °C is mostly composed of near-spherical particles with the diameter of 50–100 nm. Moreover, the SiC powder also contains very rare amount of whiskers with a diameter of 80 nm and a length of up to several micrometers. It is proposed that the present holes in the precursor particles during calcination are responsible for the formation of whiskers. Furthermore, the formation of mainly SiC near-spherical nanoparticles is ascribed to coarse surface of precursor particles during calcination, intimate contact among SiO₂ and C particles, uniformly formed free space during reduction reaction, and separation effect of unreacted carbon.     

Formation of SiC nanowhiskers by carbothermic reduction of silica with activated carbon

The silicon carbide (SiC) nanowhiskers were obtained by a carbothermic reduction of silica (SiO₂) with activated carbon at 1450 °C. The products were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). The SiC nanowhiskers were grown as crystalline β-SiC with the diameter ranging from 20 to 150 nm grew along (111) direction with the length up to several tens of micrometers. Yield of β-SiC is very high with the moderate amount of un-reacted SiO₂. This is the first report on the synthesis of high yield of β-SiC by simple direct heating method.     

Low temperature synthesis of mesoporous silicon carbide via magnesiothermic reduction

Mesoporous silicon carbides (SiC) with high surface areas (above 300 m²/g) have been prepared successfully at a relative low temperature of 650 °C via magnesiothermic reduction of mesoporous silica/carbon (SiO₂/C) composites. The physicochemical properties and the structure of the products were characterized by various techniques such as XRD, FT-IR, SEM, TEM and N₂ adsorption-desorption isotherm. The experimental results indicate that the obtained SiC materials by this new method have similar structure to corresponding silica matrix templates. It was found that the magnesium (Mg) plays an important role in determining the structure and properties of the final products, which is used as a dual role agent both reducer and catalyst. The formation mechanism of mesoporous SiC has been also discussed.     

Oxidation kinetics of SiC deposited from CH3SiCl3/H2 under CVI conditions

Oxidation tests were performed on SiC deposits prepared from CH₃SiCl₃/H₂ under chemical vapour infiltration conditions, at temperatures ranging from 900–1500 °C under a flow of pure oxygen at 100 kPa (passive oxidation regime). The kinetics of growth of the silica layer were established from thickness measurements performed by spectroreflectometry. They obey classical parabolic laws from which rate constants are calculated. Within 1000–1400 °C, the oxidation process is thermally activated with an apparent activation energy of 128 kJ mol^–1. Above 1400 °C and below 1000 °C, an increase in the activation energy is observed which is thought to be related to a change in the mechanism of the oxygen transport across the silica layer forT>1400 °C and tentatively to stress effects forT<1000 °C. The kinetics data are compared to those measured on silicon single crystals (used as a standard) and to other reported data on SiC.     

Growth of silicon carbide nanorods from the hybrid of lignin and polysiloxane using sol-gel process and polymer blend technique

We report here the formation of silicon carbide (SiC) nanorods from organic-inorganic hybrid of the commercially available lignin and sol-gel derived nanosized silica. The SiC nanorods were identified by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface morphology shows the formation of continuous nanorods of diameter in the range of 50-200 nm. The X-ray diffraction (XRD) pattern show peaks at 2θ = 35.5° and 60.2° indicate the formation of β-SiC and a sharp peak at 2θ = 22.1° suggests the presence of unreacted crystalline silica (crystoballite). The characteristic vibration of SiC at 791 cm^− 1 in Fourier transform infrared spectroscopy (FTIR) was also observed.     

SiC nanorods prepared from SiO and activated carbon

SiC nanorods with 20–100 nm diameter and 10–100 m length were synthesized by reaction between SiO and amorphous activated carbon (AAC) at 1380°C. Microstructural characterization of the SiC nanorods was carried out by high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS). The SiC nanorods grow on either a chain or from facets of SiC nanoparticles. They are usually straight and preferentially orientated along the [111] direction. Branching phenomenon exists for these nanorods. Typical SiC nanorod tip was analyzed by HRTEM image and EDS analysis. Based on an experimental analysis, a formation mechanism is proposed to explain the microstructural characterization of the SiC nanorods.     

Microwave-assisted synthesis of praseodymium hydroxide nanorods and thermal conversion to oxide nanorod

Pr(OH)₃ nanorods with uniform diameter of 12 nm and different lengths ranging from 50 to 220 nm were successfully prepared via a facile and rapid microwave-assisted hydrothermal method. Pr₆O₁₁ nanorods were also obtained from calcination of the as-prepared hydroxide nanorods as precursors at 500 °C for 6 h. The results showed that the Pr(OH)₃ with hexagonal phase and Pr₆O₁₁ nanorods with cubic phase have high crystallinity and purity. The mechanism for the microwave-assisted hydrothermal synthesis of Pr(OH)₃ nanorods was preliminarily presented.     

Nano-precipitation in hot-pressed silicon carbide

Heat treatments at 1300°C, 1400°C, 1500°C, and 1600°C in Ar were found to produce nanoscale precipitates in hot-pressed silicon carbide containing aluminum, boron, and carbon sintering additives (ABC-SiC). The precipitates were studied by transmission electron microscopy (TEM) and nano-probe energy-dispersive X-ray spectroscopy (nEDS). The precipitates were plate-like in shape, with a thickness, length and separation of only a few nanometers, and their size coarsened with increasing annealing temperature, accompanied by reduced number density. The distribution of the precipitates was uniform inside the SiC grains, but depleted zones were observed in the vicinity of the SiC grain boundaries. A coherent orientation relationship between the precipitates and the SiC matrix was found. Combined high-resolution electron microscopy, computer simulation, and nEDS identified an Al₄C₃-based structure and composition for the nano-precipitates. Most Al ions in SiC lattice exsolved as precipitates during the annealing at 1400 to 1500°C. Formation mechanism and possible influences of the nanoscale precipitates on mechanical properties are discussed.     

SiC matrix composites containing transition metal boride particulates internally synthesised by carbothermal reaction

SiC matrix composites reinforced with the various borides of the transition metals in group IV a-VI a, which were synthesized from the transition metal oxide, boron carbide and carbon mixed with SiC powder. Dense composites containing boride particulates of titanium, zirconium, niobium and chromium were prepared through reactive hot-pressing. The morphology of the internally synthesized boride particles reflected that of the starting oxide powders. SiC-NbB₂ composites with four-point flexural strength of 500 to 600 MPa and better oxidation resistance than SiC-TiB₂ were prepared even through pressureless sintering process. Pressureless-sintered and HIPed SiC-20 vol% NbB₂ exhibited the four-point flexural strength of 760 MPa at 20 °C and 820 MPa at 1400 °C.     

High temperature reactions between SiC and platinum

Solid state reactions between SiC and platinum have been studied at temperatures between 900 and 1100 °C. In the reaction zones, alternating layers of Pt₃Si and carbon, and Pt₂Si and carbon were formed at 900 and 1000 °C, respectively. Both the Pt₃Si and Pt₂Si phases were stable at respective temperatures. Annealings at 1100 °C, however, produced alternating layers of mixed Pt-silicides and carbon. The formation of platinum silicides gave rise to interfacial melting between SiC and platinum at all the temperature regimes. Laser Raman microprobe indicates that SiC decomposes into carbon and silicon at all the temperatures. The silicon reacts with platinum and forms platinum silicides, while the carbon forms clusters and stays unreacted. Based on the Raman results, the carbon exists in two different crystalline states depending upon its location from the SiC reaction interface. The reaction kinetics between SiC and platinum and the formation of periodic structure, respectively, are discussed based on the decomposition of the SiC and the phase separation of carbon from platinum silicides.     

New route to process uni-directional carbon fiber reinforced (SiC?+?ZrB2) matrix mini-composites

Unidirectional carbon fiber-reinforced (SiC + ZrB₂) matrix mini-composites were prepared by soft solution route. In this process, the matrix materials were prepared using water-soluble precursors of colloidal silica, sucrose, zirconium oxychloride, and boric acid as sources of silica, carbon, zirconia, and boron oxide respectively. The room temperature mechanical properties were investigated and the fracture features of the composites were examined. Tensile strength of 269 ± 36 MPa and fracture energy of 0.38 ± 0.05 MJ/m³ for the mini-composite, carbothermally reduced at 1,600 °C were attributed to the fiber pull out. In spite of a composite failure mode, the composite carbothermally reduced at 1,700 °C exhibited lower mechanical properties. It showed that carbon fibers reacted with ZrO₂ to form ZrC phase at 1,700 °C, formed chemical bonding, and led to a strong interface between fibers and matrix, which resulted in the degradation of mechanical properties of the mini-composites. The XRD and SEM investigations of the powders and the mini-composites revealed phase formation whereas cross-sectional microstructure indicated the uniform distribution of fibers within the matrix.     

Synthesis of beta silicon carbide powders using carbon coated fumed silica

The synthesis of beta silicon carbide (-SiC) powders by carbothermic reduction of carbon coated silica and silica mixed with carbon black was investigated. The production of -SiC powders by using carbon coated silica consists of two steps. The first step is to prepare the carbon coated silica precursor by coating fumed silica particles with carbon by pyrolytic cracking of a hydrocarbon gas (C3H6). This provides intimate contact between the reactants and yields a better distribution of carbon within the fumed silica. Fumed silica was also mechanically mixed with carbon black for comparison. Both starting mixtures were reacted in a tube furnace for 2 h at temperatures of 1300°C to 1600°C in 1 l min-1 flowing argon. The reaction products were characterized using weight loss data, X-ray diffraction (XRD), a BET surface area analyser, oxygen and free carbon analysis and transmission electron microscopy (TEM). The carbon coating process resulted in a more complete reaction, purer product and high yield SiC powders with very little agglomeration at temperatures of 1500°C and 1600°C. The -SiC powders produced at 1600°C for 2 h in argon gas flow have oxygen content of 0.3 wt%, a very fine particle size 0.1–0.3 m and uniform shape. © 1998 Chapman & Hall     

Synthesis and electrochromic study of sol-gel cuprous oxide nanoparticles accumulated on silica thin film

In this study, electrochromic properties of cuprous oxide nanoparticles, self-accumulated on the surface of a sol-gel silica thin film, have been investigated by using UV-visible spectrophotometry in a lithium-based electrolyte cell. The cuprous oxide nanoparticles showed a reversible electrochromic process with a thin film transmission reduction of about 50% in a narrow wavelength range of 400-500 nm, as compared to the bleached state of the film. Using optical transmission measurement, we have found that the band gap energy of the films reduced from 2.7 eV for Cu₂O to 1.3 eV for CuO by increasing the annealing temperature from 220 to 300 °C in an N₂ environment for 1 h. Study of the band gaps of the as-deposited, colored and bleached states of the nanoparticles showed that the electrochromic process corresponded to a reversible red-ox conversion of Cu₂O to CuO on the film surface, in addition to the reversible red-ox reaction of the Cu₂O film. X-ray photoelectron spectroscopy indicated that the copper oxide nanoparticles accumulated on the film surface, after annealing the samples at 200 °C. Surface morphology of the films and particle size of the surface copper oxides have also been studied by atomic force microscopy analysis. The copper oxide nanoparticles with average size of about 100 nm increased the surface area ratio and surface roughness of the silica films from 2.2% and 0.8 nm to 51% and 21 nm, respectively.     

Synthesis of β-silicon carbide nanofiber from an exfoliated graphite and amorphous silica

Silicon carbide (SiC) nanofibers were synthesized from exfoliated graphite containing silica particles at 1425 °C in a 25% H₂/Ar atmosphere. Two types of SiC nanofibers with different morphologies were formed depending on the silica content. A higher silica content led to straight nanofibers with a regular diameter size. The SiC nanofibers derived from the exfoliated graphite/40 wt% SiO₂ powder mixture contained a large number of stacking faults and grew along the [1 1 1] direction. A gas–gas reaction mechanism was proposed to explain the formation of SiC nanofibers.     

Preparation of β-MnO2 nanorods through a γ-MnOOH precursor route

A new MnOOH precursor route has been developed to synthesize single-crystalline nanorods of tetragonal β-MnO₂. Uniform γ-MnOOH nanorods were first prepared by reducing KMnO₄ with KI under hydrothermal conditions at 120 °C. After calcination of the γ-MnOOH nanorods at 250 °C for 2 h in air, β-MnO₂ nanorods retaining the morphologies of γ-MnOOH nanorods were obtained. The temperature, time and heating speed of calcination were found to be important for the morphologies of the β-MnO₂ nanorods.     

CdS microflowers and interpenetrated nanorods grown on Si substrate: Structural,optical properties and growth mechanism

CdS semiconductor with different morphologies have been achieved by simple thermal evaporation of CdS powder at 1050 °C in a flowing Ar atmosphere. The products were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy and Photoluminescence. microflowers and interpenetrative nanorods of CdS were formed on catalyst free Si wafers at a temperature of 700 °C and 600 °C respectively. The flower like structures are composed of many interleaving nanorods which have the uniform diameter of about 700 nm and a well crystalline structure with [0001] as growth direction. The interpenetrative nanorods are found to be bounded with six side facets. X-ray diffraction studies revealed the hexagonal structure in both the products. The formation mechanism of microflowers and interpenetrated nanorods was discussed on the basis of nucleation growth kinetics. Room temperature photoluminescence spectra showed a strong green emission band (at ∼510 nm) from the CdS flower like structures, but on the other hand a red emission shoulder along with strong green emission band was observed for interpenetrative nanorods. These CdS micro/nanostructures with abundant morphologies may find applications in various micro/nanodevices, and the kinetics-driven morphology might be exploited to synthesize similar structures of other functional II–VI semiconductors.     

Fabrication of single-crystalline Co3O4 nanorods via a low-temperature solvothermal process

Co₃O₄ nanorods with average diameter and length of ∼ 50 nm and 1 μm were successfully prepared via a simple surfactant-assisted solvothermal method at 160 °C for 12 h. The formation of Co₃O₄ nanorods is attributed to alcoholysis of cobalt ions dispersed in ethanol in the presence of a capping agent—CTAB. The composition and purity of the sample were characterized by X-ray diffraction (XRD). Transmission and scanning electron microscopy images show that the particles are homogenous and have the shape of rods. The mechanism of forming Co₃O₄ nanorods is also discussed.     

Multi-layer CVD-SiC/MoSi2–CrSi2–Si/B-modified SiC oxidation protective coating for carbon/carbon composites

To further improve the oxidation resistance of coating for carbon/carbon (C/C) composites, a multi-layer CVD-SiC/MoSi₂–CrSi₂–Si/B-modified SiC coating was prepared on the surface of C/C composites by pack cementation and chemical vapour deposition method, respectively. The microstructures, oxidation and thermal shock resistance of the coating were studied. The influence of B content in pack powder on the microstructure and oxidation resistance of B-modified SiC coating was also investigated. The results show that the B-modified SiC coating prepared with 10 wt.% B exhibited the best oxidation protection ability for C/C composites at 1173 K. The multi-layer coatings could protect the C/C composites at 1173 K for 30 h and 1873 K for 200 h, and endure 30 thermal cycles between 1873 K and room temperatures. The oxidation resistance and thermal shock resistance is mainly attributed to their dense structure and self-sealing property.     

Deposition and microhardness of SiC from the Si2Cl6-C3H8-H2-Ar system

We obtained SiC coating layers on a graphite substrate using hexachlorodisilane (Si₂Cl₆, boiling point 144° C) as a silicon source and propane as a carbon source. We examined the deposition conditions, contents of carbon, silicon and chlorine in the deposits, and the microhardness. Mirror-like amorphous silicon layers were deposited in the reaction temperature range 500 to 630° C. well-formed silicon carbide layers with good adherency to the substrate were obtained above 850° C. The lowest deposition temperature of SiC was estimated to be 750 to 800° C. The Vickers microhardness of the SiC layer was about 3800 kg mm^–2 at room temperature and 2150 kg mm^–2 at 1000° C.